In general, electrophotography in a PPC (Plain Paper Copy) copier or printer for transferring a toner image formed on a photo-sensitive material to recording paper is carried out in the procedure described below. First, an electrostatic latent image is formed on the photo-sensitive material, the latent image is developed by using a toner, the toner image is transferred onto a sheet to be fixed such as paper or the like, and then the transferred toner image is fixed by heating with a heat roll or a film. Since the fixation is carried out under heat in a state that the heat roll or the film is directly brought into contact with the toner on the sheet to be fixed according to this method, it is performed in a short period of time and with a very high thermal efficiency, thereby achieving a very good fixing efficiency. However, though having a good thermal efficiency, the heat fixing method has a problem of a so-called offset phenomenon since the toner is brought into contact with the surface of the heat roll or the film in the melt state.
In order to obtain a resin excellent in the fixing properties and offset resistance, there has been known a resin obtained by using a high molecular weight resin and a low molecular weight resin in mixture and crosslinking a high molecular weight portion. Furthermore, to exhibit both the low temperature fixing properties and offset resistance, various techniques have been disclosed in the documents (for example, Patent Documents 1 to 4). However, these documents disclose a design suitable for a toner for monochrome use. The techniques disclosed in these documents are effective in both the low temperature fixing properties and offset resistance, but a design different from that of a toner for monochrome use is required when such a toner is applied to a color toner.
Gloss is required as an object to achieve specific to a color toner. When a toner for monochrome use is applied to a color toner, there has been still room for improvement in view of the gloss. In particular, even though a toner for monochrome use requires high elasticity in order to improve offset resistance, there has been a problem such that the unevenness on the printed surface in the color toner is caused, thereby impairing the gloss.
In Patent Document 5, there has been disclosed a binder resin without containing a gel portion, while in Patent Document 6, there has been disclosed a color toner having the content of a gel component of less than 5 weight %. However, in these documents, since the range of Mw/Mn is narrow, offset resistance is not sufficient. Therefore, there is room for improvement in balancing the gloss and offset resistance. Furthermore, when a high molecular component ratio and gel content are reduced in order to enhance the gloss, there is also a problem of reduction of durability.
Patent Document 1: Japanese Patent Laid-open No. 2002-189316
Patent Document 2: Japanese Patent Laid-open No. 2004-144860
Patent Document 3: Japanese Patent Laid-open No. H10-90943
Patent Document 4: International Publication Pamphlet No. 2004-015498
Patent Document 5: Japanese Patent Laid-open No. 2004-177969
Patent Document 6: Japanese Patent Laid-open No. H10-171162